Among the various video display systems available in the art, an optical projection system is known to be capable of providing high quality displays in a large scale. In such an optical projection system, light from a lamp is uniformly illuminated onto an array of, e.g., M.times.N, actuated mirrors, wherein each of the mirrors is coupled with each of the actuators. The actuators may be made of an electrodisplacive material such as a piezoelectric or an electrostrictive material which deforms in response to an electric field applied thereto.
The reflected light beam from each of the mirrors is incident upon an aperture of, e.g., an optical baffle. By applying an electric signal to each of the actuators, the relative position of each of the mirrors to the incident light beam is altered, thereby causing a deviation in the optical path of the reflected beam from each of the mirrors. As the optical path of each of the reflected beams is varied, the amount of light reflected from each of the mirrors which passes through the aperture is changed, thereby modulating the intensity of the beam. The modulated beams through the aperture are transmitted onto a projection screen via an appropriate optical device such as a projection lens, to thereby display an image thereon.
In FIG. 1, there is a top view setting forth an array 100 of M.times.N thin film actuated mirrors 101, wherein M and N are integers, for use in an optical projection system, disclosed in a copending commonly owned application, U.S. Ser. No. 08/602,928, entitled "THIN FILM ACTUATED MIRROR ARRAY FOR USE IN AN OPTICAL PROJECTION SYSTEM".
In FIGS. 2A and 2B, there are provided with schematic cross sectional views taken along lines 2A--2A and taken along lines 2B--2B in FIG. 1, respectively.
The array 100 includes an active matrix 110, a passivation layer 120, an etchant stopping layer 130 and an array of M.times.N actuating structures 200.
The active matrix 110 includes a substrate 112, an array of M.times.N transistors (not shown) and an array of M.times.N connecting terminals 114.
The passivation layer 120, made of, e.g., a phosphorsilicate glass (PSG) or silicon nitride, and having a thickness of 0.1-2 .mu.m, is located on top of the active matrix 110.
The etchant stopping layer 130, made of silicon nitride, and having a thickness of 0.1-2 .mu.m, is positioned on top of the passivation layer 120.
Each of the actuating structures 200 is provided with a first thin film electrode 185, a thin film electrodisplacive member 175, a second thin film electrode 165, an elastic member 155 and a conduit 195. The first thin film electrode 185 made of an electrically conducting and light reflecting material is located on top of the thin film electrodisplacive member 175 and is electrically connected to ground, thereby functioning as a mirror as well as a common bias electrode. The thin film electrodisplacive member 175 made of a piezoelectric material or an electrostrictive material is placed on top of the second thin film electrode 165. The second thin film electrode 165 made of an electrically conducting material is located on top of the elastic member 155, is electrically connected to a corresponding transistor through the conduit 195 and the connecting terminal 114, and is disconnected electrically from the second thin film electrode 165 in other thin film actuated mirrors 101, thereby allowing it to function as a signal electrode. The elastic member 155, made of a nitride, is positioned below the second thin film electrode 165. The conduit 195, made of a metal, extends from top of the thin film electrodisplacive member 175 to top of a corresponding connecting terminal 114. The conduit 195 extending downward from top of the thin film electrodisplacive member 175 and the first thin film electrode 185 placed on top of the thin film electrodisplacive member 175 in each of the thin film actuated mirrors 101 are not electrically connected to each other. Each of the actuating structures 200 has a proximal end 210 and a distal end 220, the proximal end being divided into a first and second side portions 212, 214. A bottom portion at the proximal 210 end thereof is attached to top of the active matrix 110, with the etchant stopping 130 and the passivation layers 120 partially intervening therebetween, thereby cantilevering the actuating structure 200.
There are certain deficiencies associated with the above described the array 100 of M.times.N thin film actuated mirrors 101. Since a bottom portion at the proximal end 210 in each of the actuating structures 200 is attached to top of the active matrix 110 in order to cantilever the actuating structure and each of the connecting terminals 114 of the active matrix 110 is located below the first side portion 212 of the proximal end 210, the top of the first side portion 212 in the proximal end 210 is different from that of the second side portion 214 in the proximal end 210 thereof in such a way that the actuating structure 200 becomes slanted.